As an image display device, there are many image devices available on the market like a TV, PC, Projector, video camera, cellular phone etc, but there is a limit to a size in these conventional image display devices, so an image of a wide area that human eyes are actually able to see cannot be obtained from these image display devices. Further, as a portable image display device, an eyeglass-type image display and head-mounted image display devices that are called a wearable display device have been known.
As for the wearable image display, as shown in FIG. 40, a method in which small half mirror 40 is arranged at a portion of field of view and an image output from image output element 39 such as a plasma display device, LCD etc is deflected by half mirror 40 via projection optical system 38, and the image is projected on a retina has been known. This is a method that uses the half mirror, so that the image output from image output element 39 looks like floating on a portion of field of view (a first type). However, as for a viewing angle, only an order of a few degrees is obtainable, so that this method is a candidate for use in displaying information of a screen of the cellular phone etc.
Also, as for a method for getting a little bit larger image information than that of the cellular phone, there is a method as shown in FIG. 6 (b) in which an image output from image output element 39 is projected on the retina of the eyeball via a plurality of reflection surfaces and projection optical system 42 by arranging large optical element 41 in front of at least one of eyeballs.
In such the method, a relatively large viewing angle (order of 15–30 degrees) is obtained, but only an image display device of which field of view is completely shielded has been proposed. Thus, a second-type image display device that is arranged detachably in front of one eye of two eyes and used as an image display device of a wearable PC and a third-type image display device in which a same image display device is separately arranged with respect to both eyes and used instead of a TV and projector have been proposed.
The foregoing three types of the image display device have been expected as a wearable image display device in place of the cellular phone, note-size PC, TV and projector of the prior art. In fact, these image display devices have an advantage in “wearable”, but a size of field of view of them is actually not very different from one of the conventional display devices and, when considering difficulty in wearing, eyestrain due to a blocked field of view, a weight mounted over ears and head etc, they have a shortcoming that these disadvantages are conspicuous.
This invention is made in view of these circumstances and an object of this invention is to provide an image display device that is wearable or usable in proximity to at least one of eyes having a large viewing angle close to field of view with which a user sees, and a projection optical system that is arranged in front of user's eyes and projects an image on the eyeball.